Low end firepower and shield output for an Imperial Star Destroyer.

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The Merchant
In Star Wars a controversial topic is the firepower and shield output of an Imperial Star Destroyer. While some like to simply use the Technical manuals (which is akin to using Databook info) to know the power of a ship, others resent the idea. And of course there are methods such as scaling from the Death Star which people conclude is too much of a high end. So here's the Firepower/Shield strength for an Imperial Star Destroyer-II. This is going to determine a solid low end for an ISD.

For those who don't want to read the whole thing here's the summary:
Shields: 7200 Megatons of TNT overall, 20 Megatons does nothing.
No shields: Less than 106 Megatons of TNT.
Point Defense Laser Cannons: Roughly 386 Kilotons of TNT.
Heavy Turbolasers: roughly 48 Megatons of TNT.


In the video the Star Destroyer's vaporize asteroids that were scaled to be roughly 40 meters in diameter according to the Turbolaser commentaries.
According to


A 40 meter in diameter sphere will have a volume of 33510.32567 Cubic meters. Asteroids usually have a Nickel-Iron composition, for a low end I will assume the asteroids have a density of Iron. Density of Iron is 7870 Kilograms per cubic meter.
33510.32567 x 7870 equals 263726263.023 Kilograms for the mass of the Asteroids. According to:


Heat of vaporization for Iron is 61.2E+5 Joules per Kilogram. Therefore to vaporize the asteroid:

263726263.023 x 61.2E+5 equals 1.6140047e+15 Joules of energy, or 385.756381 Kilotons of TNT to vaporize the asteroids. That's the firepower of a point defense gun on the ISD. According to Stardestroyer.net those guns in comparison to the huge Heavy turbolasers on top of the ISD is roughly 125 times smaller. So if firepower correlates to size the Heavy turbolasers would be able to dish out 48219.547625 Kilotons of TNT.

We also see an Asteroid hit the ISD and vaporizing upon impact of the ISD's shields. According to:

Average speed of an asteroid is 25 Kilometers per second.

And using:


The impact of a 40 meter asteroid would have a yield roughly equal to 8.241E+16 Joules or roughly 20 Megatons of TNT.
Later we see an asteroid that was calc'd being 70 meters in diameter hitting the bridge of a Star Destroyer:


A 70 meter asteroid would have a volume of 179594.40164 cubic meters and a mass of 1413407940.91 Kilograms. An asteroid going at that speed would have an impact roughly equal to a 106 Megaton yield. While it did seem to take out the bridge the Star Destroyers were in the field for an unknown amount of time, which would mean the damage would accumulate enough for an asteroid of that size to be able to penetrate the shields. Assuming 1 hour has passed and every 10 seconds an asteroid of 40 meters in diameter hit the Destroyer
1 hour equals 3600 seconds. Divide by 10 and that would mean 360 asteroids have hit the Asteroid during that hour. 360 x 20 Megatons would be 7200 Megatons of total "firepower" the Star Destroyers endured before their shields started to take a toll.

Anyways yeah.

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